An optical transceiver is frequently used in a transmission system conducting optical fiber communications. The optical transceiver includes an optical transmitter and an optical receiver. The optical transmitter converts an electric signal into an optical signal, and transmits the optical signal to an optical waveguide, such as optical fiber. As a system of converting an electric signal to an optical signal, there is a system using a light source and an optical modulator. The light source is a semiconductor laser or the like, and outputs CW (Continuous Wave) light. The optical modulator modulates the CW light output from the light source according to an electric signal (a driving signal), and outputs a modulated optical signal. A driving circuit is used to drive the optical modulator. The driving circuit generates a driving voltage according to the electric signal and supplies a bias voltage serving as a reference voltage of the driving voltage.
Since the electric signal drives the driving circuit at high speed, a reflection coefficient of the driving circuit needs to be suppressed up to a frequency of, for example, about 40 [GHz]. Further, a high common-mode rejection ratio is required as circuit performance for high speed communication.